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Results for “Population Density--statistics”

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PubMed2001

Genetic variation for preadult viability in Drosophila melanogaster.

The extent of genetic variation in fitness and its components and genetic variation's dependence on environmental conditions remain key issues in evolutionary biology. We present measurements of genetic variation in preadult viability in a laboratory-adapted population of Drosophila melanogaster, made at four different densities. By crossing flies heterozygous for a wild-type chromosome and one of two different balancers (TM1, TM2), we measure both heterozygous (TM1/+, TM2/+) and homozygous (+/+) viability relative to a standard genotype (TM1/TM2). Forty wild-type chromosomes were tested, of which 10 were chosen to be homozygous viable. The mean numbers produced varied significantly between chromosome lines, with an estimated between-line variance in log(e) numbers of 0.013. Relative viabilities also varied significantly across chromosome lines, with a variance in log(e) homozygous viability of 1.76 and of log(e) heterozygous viability of 0.165. The between-line variance for numbers emerging increased with density, from 0.009 at lowest density to 0.079 at highest. The genetic variance in relative viability increases with density, but not significantly. Overall, the effects of different chromosomes on relative viability were remarkably consistent across densities and across the two heterozygous genotypes (TM1, TM2). The 10 lines that carried homozygous viable wild-type chromosomes produced significantly more adults than the 30 lethal lines at low density and significantly fewer adults at the highest density. Similarly, there was a positive correlation between heterozygous viability and mean numbers at low density, but a negative correlation at high density.

Animals↗
PubMed1975

The statistical analysis of density dependence.

The distrubution of the reciprocal of von Neumann's ratio is considered under the random walk model, x(t+1) rwis;d xt + et, and it is shown how this quantity can be used to test for density dependence in animal populations. Another test is described which is robust under superimposed errors of measurement. The methods are used to analyze data on Canadian fur-bearing mammals.

Animals↗
PubMed1973

Adult population estimate of Toxorhynchites brevipalpis.

An estimate of the numbers of adults of the predacious mosquito Toxorhynchites brevipalpis was made in a 1-ha biotope in Dar es Salaam, Tanzania, where the population of its larval prey Aedes aegypti was high, by means of the mark-release-recapture method. Two months after the end of the rainy season, the number of adults was estimated to be 3 500-about 6 times the number of adult A. aegypti in the biotope.

Aedes↗
PubMed1981

Computation of cancer incidence rates for defined small geographical areas--matching of numerator and denominator.

The authors present the problem of validity of numerator and pertinence of denominator for small geographical areas on sample of average annual crude incidence rates of stomach cancer in Slovenia during the period 1968--1974. At census in 1971 this country counted 1 727 137 of population. According to the residence of the patients the rates have been calculated for 60 municipalities, and besides for 29 so called "epidemiological regions", defined by their geographical and ethnic characteristics. Although in both instances great differences in incidence rates have been found, only a few areal units exhibited a significantly lower or higher rate from the national average. Specially areas with small population base "disappeared" in the average, although the value of the rate for them was rather low or high. A formula is presented by which at given rate for total country it is possible to determine the minimal size of population which still could provide estimation of statistically significant lower rate. Thus, for areas with small population a period of observation through many years is required in order to obtain the necessary minimal population base. The question is pointed out, whether this approach is reasonable as to the epidemiological interest, considering that some factors related to cancer may change during the long period of time. On the other hand, when merging small areas into larger ones, attention must be paid that these are not too heterogeneous as to their cancer incidence rate, geographical, ethnic, socio-economic and life-style features.

Humans↗
PubMed1976

Mathematical models for nonparametric inferences from line transect data.

A general mathematical theory of line transects is develoepd which supplies a framework for nonparametric density estimation based on either right angle or sighting distances. The probability of observing a point given its right angle distance (y) from the line is generalized to an arbitrary function g(y). Given only that g(O) = 1, it is shown there are nonparametric approaches to density estimation using the observed right angle distances. The model is then generalized to include sighting distances (r). Let f(y/r) be the conditional distribution of right angle distance given sighting distance. It is shown that nonparametric estimation based only on sighting distances requires we know the transformation of r given by f(O/r).

Animals↗
PubMed1984

Research design and analysis of data procedures for predicting body density.

Statistical methods used to develop body composition prediction equations were examined. Equations published in the 1960s and early 1970s have been called "population-specific" equations because they were developed on homogeneous samples. A major limitation of population-specific equations was a low ratio of subjects per variable, which reduces validity. The more recent method has been to develop "generalized" equations with large samples varying greatly in age and body fatness. The statistical models used for generalized equations were nonlinear regression analysis to account for the quadratic relation between body density and skinfold fat. Age was used as an independent variable to adjust for aging. Generalized equations exhibit accuracy consistent with population-specific equations and increase the generalizability of prediction. Future body composition research should focus on the cross-validation of published equations to define the limits of equation accuracy.

Adult↗
PubMed1984

Averaging population density.

Population density is a commonly quoted statistic. Almost no general descriptive summary of the population of an area is complete without a density listing, table or map. As each such density statistic is an average, it is worth considering what kind of average is being used. This article analyzes this and illustrates the effect of some alternative calculations using population density data for Great Britain; the findings, however, are of general validity.

Demography↗